1. Field of the Invention
The present invention relates to a light emitting device and an illumination apparatus using the light emitting device.
2. Description of Related Art
In recent years, a light emitting diode (LED) device configured to emit white-system light by a combination of a blue LED element and a yellow fluorescent member having a complementary chromatic relationship to blue light emitted from the blue LED element, has been marketed as a package with a high light intensity.
However, there is a problem that the LED device has low color rendering properties and color rendering properties show an index representing the naturalness of color obtained when illuminating. That is to say, because both green and red spectrum components are not included or sufficient in the combination of the blue LED element and the yellow fluorescent member, it has not been possible to obtain sufficient color rendering properties for a backlight of a liquid crystal display, light source for illumination, or the like.
Therefore, what has conventionally been proposed is a light emitting device which is configured to emit the three primary colors and improve the color rendering properties by dispersing both a green fluorescent material 3 and a red fluorescent material 4 in a sealing body 2 covering a blue LED element 1, as shown, for example, in FIG. 7A (see, for reference, Japanese Patent Laid-Open No. 2001-144331, claims and FIG. 13).
There has also been proposed a light emitting device which is configured to emit the three primary colors and improve the color rendering properties by dispersing each of a blue fluorescent material 7, a green fluorescent material 3 and a red fluorescent material 4 in a sealing body 6 covering an ultraviolet LED element 5, as shown, for example, in FIG. 7B (see, for reference, Japanese Patent Laid-Open No. 2004-127988, claims and FIG. 2).
However, the following problems may be experienced with the above-mentioned light emitting devices.
The conventional light emitting devices including the combination of a single color LED element such as the blue LED element 1 or ultraviolet LED element 5 and a plurality of fluorescent material such as the blue, green and red fluorescent material 3, 4, 7 and configured to obtain the three primary colors have sufficient color rendering properties, but have low emission efficiency making it difficult to obtain the required light intensity.
In other words, the plurality of the fluorescent material having different colors must be excited by a single color of the single LED element. Accordingly, a high brightness is required for light emitted from the single LED element. In addition, because each of the fluorescent material has a different emission efficiency with respect to the single color of light, it is not possible to obtain sufficient light intensity and good color rendering properties for the light emitting device.